On Demand Carbon Monoxide Generator For Therapeutic and Other Applications

ABSTRACT

A device that can produce carbon monoxide for therapeutic and laboratory applications is disclosed. The device includes and electrochemical cell that converts carbon dioxide or a carbon dioxide containing molecule such as a carbonate or bicarbonate or bicarbonate into carbon monoxide and oxygen. The cell contains additives so pure carbon monoxide is obtained.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit under 35 U.S.C.§119(e) to U.S. Provisional Application 61/540,044, entitled “On DemandCarbon Monoxide Generator for Therapeutic and Other Applications,” filedSep.28, 2011. This application is related to U.S. Non-Provisional PatentApplication US 2011/0237830 filed Jul. 4, 2010, entitled “Novel CatalystMixtures,” which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/317,955 filed Mar. 26, 2010, entitled “NovelCatalyst Mixtures,” and the application is also related to internationalapplication WO 2011/120021, entitled “Novel Catalyst Mixtures,” filedMar. 25, 2011, which claims the benefit of both of the aboveapplications. This application is also related to international patentapplication WO201206240, “Novel Catalyst Mixtures,” filed Jul. 1, 2011,which claims the benefit of above applications US 2011/0237830 and WO2011/120021, and which also claims the benefit of U.S. ProvisionalPatent Application 61/484,072, “Novel Catalyst Mixtures,” filed May 9,2011, and U.S. Non-Provisional patent application Ser. No. 13/174,365,“Novel Catalyst Mixtures,” filed Jun. 30, 2011. The present applicationis also related to U.S. Provisional Application 61/499,225, entitled“Low Cost Carbon Dioxide Sensors,” filed Jun. 29, 2011, and U.S.Provisional Application 61/540,044, entitled “On Demand Carbon MonoxideGenerator for Therapeutic and Other Applications,” filed Sep. 28, 2011.The present application is also related to U.S. patent application Ser.No. 13/530,058 entitled “Sensors for Carbon Dioxide and Other End Uses,”filed Jun. 21, 2012, which claims benefit from each of theaforementioned patent applications and provisional patents. The presentapplication is also related to continuation-in-part application U.S.Ser. No. 13/445,887, “Electrocatalysts for Carbon Dioxide Conversion,”filed Apr. 12, 2012, which is based on the above U.S. Non-ProvisionalPatent Application US 2011-0237830 filed Jul. 4, 2010. In addition, thepresent application is related to international patent applicationPCT/US12/43651, “Low Cost Carbon Dioxide Sensors,” filed Jun. 21, 2012,which claims the benefit of the above U.S. Provisional PatentApplication 61/499,255, entitled “Low Cost Carbon Dioxide Sensors,”filed Jun. 29, 2011. Each of the above applications is herebyincorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made, at least in part, with U.S. government supportunder Department of Energy Grant DE-SC0004453. The U.S. government hascertain rights in the invention.

FIELD OF THE INVENTION

This patent relates to a system for the production of carbon monoxide ondemand. The devices of this invention are applicable, for example, forproduction of carbon monoxide in chemical laboratories or therapeuticsettings.

BACKGROUND

Carbon monoxide (CO) is widely used as an industrial chemical, inchemical laboratories. Clinical applications of CO are just starting toappear. There are many chemical processes to generate carbon monoxide onan industrial scale such as those disclosed in U.S. Pat. Nos. 2,218,262,2,665,972, 3,046,093, and 4,564,513. However, clinical and laboratoryapplications still rely on gas cylinders to supply carbon monoxide.Carbon monoxide is poisonous and if a cylinder leaks it could lead tohazardous conditions. Further, cylinders are not a convenient deliverymode in a clinical application.

At present there is a need for a carbon monoxide delivery system thatdoes not rely on gas cylinders, and instead creates carbon monoxide ondemand.

A few previous carbon monoxide generators have been disclosed. Forexample, U.S. Pat. Nos. 6,948,352, 7,951,273, and patent application2005/0100478 disclose devices that are able to generate nanograms/hr ofcarbon monoxide for calibration purposes, but the devices cannot producethe mg/min of carbon monoxide needed for some clinical applications.Also, the reactions in the devices produce toxic byproducts when theyare run at the mg/min scale.

Patent application US 2011/0217226 provides a method to convert formicacid to carbon monoxide, but formic acid is corrosive to mucusmembranes. Traces of formic acid can be released from the device whencartridges are changed or during a device failure, which would not bepreferred for inhalation therapy.

There are also a number of electrochemical processes that convert CO₂ orother compounds into a variety of products including carbon monoxide, asoutlined in U.S. Pat. Nos. 3,959,094, 4,240,882, 4,523,981, 4,545,872,4,595,465, 4,608,132, 4,608,133, 4,609,440, 4,609,441, 4,609,451,4,620,906, 4,668,349, 4,673,473, 4,711,708, 4,756,807, 4,818,353,5,064,733, 5,284,563, 5,382,332, 5,457,079, 5,709,789, 5,928,806,5,952,540, 6,024,855, 6,660,680, 6,987,134, 7,157,404, 7,378,561,7,479,570, and the papers reviewed by Hori (Modern Aspects ofElectrochemistry, 42, 89-189, 2008) (“the Hori Review”), Gattrell, etal. (Journal of Electroanalytical Chemistry, 594, 1-19, 2006) (“theGattrell review”), DuBois (Encyclopedia of Electrochemistry, 7a,202-225, 2006) (“the DuBois review”). None of the previously disclosedelectrochemical methods produce carbon monoxide at purities suitable forclinical applications. In particular, most of the previous processesproduce acid or organic byproducts. Further, the Hori review indicatesthat all of the electrochemical systems developed so far produce streamsthat are less than 90% CO. For example, the Hori review shows that underthe best conditions a gold or silver working electrode produces a COstream that contains over 10% hydrogen, and about 1% of acetic acid. Theacetic acid would preclude the use of the device in inhalation therapy,and the high hydrogen concentration would create an explosion hazardwhen the stream is mixed with oxygen for inhalation therapy.

SUMMARY OF THE INVENTION

The invention provides a new carbon dioxide generator design that canproduce carbon monoxide on demand at the mg/min rate needed for clinicalapplications, at the purities needed for these applications, and doesnot use any corrosive or toxic starting materials. The general approachis to start with carbon dioxide or a related carbonate or bicarbonate,and use a device to convert that material into carbon monoxide (CO) ondemand. The advantage is that one does not use any toxic or corrosivestarting materials, so the process is safe even if there is a smallleak.

The device may include an electrochemical cell with a working electrode,a counter electrode, and an electrolyte in between, wherein theelectrochemical cell is active for CO₂ reduction to carbon monoxide andoxygen. One supplies either CO₂ or a CO₂ containing compound such as acarbonate or bicarbonate to the working electrode, and applies a voltagebetween the working electrode and the counter electrode to producecarbon monoxide at a controlled rate.

The system may also include a means to control the rate of production ofcarbon monoxide. Electrochemical devices are particularly preferredsince one can precisely control the rate of carbon monoxide productionby controlling either the voltage or current to the electrochemicalcell.

Examples of reactions that may occur on the working electrode of anelectrochemical device include:

CO₂+2e−→CO+½O₂ ²⁻

CO₂+2H⁺+2e−→CO+H₂O

CO₂+H₂O+2e−→CO+2OH⁻

HCO₃ ⁻+H₂O+e−→CO+2OH⁻

HCO₃ ⁻+3H⁺+2e−→CO+2H₂O

where e− is an electron. The examples given above are merelyillustrative and are not meant to be an exhaustive list of all possiblereactions on the working electrode.

Key to the invention is the discovery of a catalyst mixture for theworking electrode that produces at least 20 times more CO than hydrogen,and does not produce significant quantities of other impurities. Thecatalyst mixture may include components that enhance the rate of COformation and/or decrease the rate of hydrogen formation. The catalystmixture may include at least one Catalytically Active Element, and atleast one Helper Catalyst and/or Hydrogen Suppressor. The HelperCatalyst can include, for example salts of choline, or cholinederivatives or EMIM and its derivatives. When the Catalytically ActiveElement and the Helper Catalyst are combined, the rate and/orselectivity of a chemical reaction to produce CO can be enhanced overthe rate seen in the absence of the Helper Catalyst. For example, theoverpotential for electrochemical conversion of carbon dioxide to CO canbe substantially reduced, and the current efficiency (namely,selectivity) for CO₂ conversion can be substantially increased.

In one aspect, the present invention includes an electrochemical cellwith a fluid phase, the cell including a hydrogen evolution suppressormaterial. It is preferred that the hydrogen suppressor has a vaporpressure of less than 10⁻² ton so as to not substantially contaminatethe product stream. The hydrogen evolution suppressor may include atleast one positively charged nitrogen or phosphorus atom in itsstructure. The nitrogen could be, for example, part of a quaternaryamine group or an imidizolium. The hydrogen suppressor molecules canalso have at least one polar group selected from the group consisting of—OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently canbe H or a linear, branched, or cyclic C₁-C₄ aliphatic group, and X is ahalide, such as chlorine or fluorine. In particular, the polar group orgroups can include at least one hydroxyl group and/or at least onehalide atoms, but these molecules would preferably not contain acarboxylic acid group or be ionic salts of a carboxylic acid, sincethese can lead to acid byproducts. An example of such a hydrogenevolution suppressor molecule would be a salt including the cholinecation, or a choline derivative of the form R₁R₂R₃N⁺(CH₂)_(n)OH orR₁R₂R₃N⁺(CH₂)_(n)Cl, wherein n=1-4, and R₁, R₂, and R₃ are independentlyselected from the group consisting of aliphatic C₁-C₄ groups, —CH₂OH,—CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, and —CH₂COCH₃and molecules where one or more chlorine or fluorine is substituted forhydrogen in aliphatic C₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH,—CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, or —CH₂COCH₃. The electrochemical cellcan also include a Catalytically Active Element, which could be at leastone of the following chemical elements: V, Cr, Mn, Fe, Co, Ni, Cu, Sn,Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si,C, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Nd.

In another aspect, the present invention includes a method ofsuppressing hydrogen gas evolution from water that might be present in asystem to create carbon monoxide on demand, the method including thesteps of: (i) providing an electrochemical cell having a fluid phase anda negative electrode, (ii) providing in the fluid phase a hydrogenevolution suppressor as described above that includes a cationcontaining at least one positively charged nitrogen or phosphorus groupand at least one polar group selected from the group consisting of —OR,—COR, —COOR, —NR₂, —PR₂, —SR and X, where each R independently can be Hor a linear, branched, or cyclic C₁-C₄ aliphatic group, and X is ahalide, and (iii) operating the electrochemical cell with the negativeelectrode at a potential that would cause hydrogen gas evolution fromwater that might be present in an electrochemical cell if the hydrogenevolution suppressor were not present. The electrochemical cell could beas described in the previous paragraph.

In yet another aspect, the present invention includes a carbon monoxidegenerator that includes an Active Element, Helper Catalyst Mixture, inwhich the addition of the Helper Catalyst improves the rate or yield ofCO production, while simultaneously decreasing the rate or yield of theundesired side reactions. The undesired reaction may be the evolution ofhydrogen gas or the creation of some poisonous impurity. The HelperCatalyst can include a cation containing at least one positively chargednitrogen or phosphorus group and at least one polar group selected fromthe group consisting of —OR, —COR, —COOR, —NR₂, —PR₂, —SR and X, whereeach R independently can be H or a linear, branched, or cyclic C₁-C₄aliphatic group, —COOR is not a carboxylic acid, and X is a halide. Forexample, the cation could contain at least one quaternary amine groupand at least one halide or hydroxyl group, but no carboxylic acid groupor carboxylic acid salt. The quaternary amine cation can be, forexample, choline cations, or choline cation derivatives of the formR₁R₂R₃N⁺(CH₂)_(n)OH or R₁R₂R₃N⁺(CH₂)_(n)Cl, where n=1-4, and R₁, R₂, andR₃ are independently selected from the group that includes aliphaticC₁-C₄ groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH —CH₂CHOHCH₃ , —CH₂COH,—CH₂CH₂COH, and —CH₂COCH₃ and molecules where one or more chlorine orfluorine is substituted for hydrogen in aliphatic C₁-C₄ groups, —CH₂OH,—CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, and —CH₂COCH₃

In still another aspect of the present invention, this applicationdiscloses a catalyst mixture having a Catalytically Active Element and aHelper Catalyst in which the Helper Catalyst also functions as adirector molecule. The Helper Catalyst/director molecule would be amolecule containing at least one positively charged group and at leastone group for surface attachment. The positively charged group can be,for example, a phosphonium group, or an amine group, such as aquaternary amine. The group for surface attachment can be, for example,a polar group selected from the group consisting of —OR, —COR, —COOR,—NR₂, —PR₂, —SR and X, where each R independently can be H or a linear,branched, or cyclic C₁-C₄ aliphatic group, —COOR is not a carboxylicacid, and X is a halide.

In still another aspect of the invention, this application discloses acarbon monoxide generator that includes a removable cartridge containingCO₂ or a chemical compound containing CO₂ such as a carbonate orbicarbonate, and a means to convert CO₂ to CO with hydrogenconcentrations below 5% of the CO concentration, and less than 5 ppm ofacetic acid or other impurities.

Finally the invention is not limited to the production of CO. A similardesign with other reactants may be used as a generator for othertherapeutic gases such as nitric oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical electrochemical cell.

FIG. 2 is a schematic diagram of how the potential of the system changesas it proceeds along the reaction coordinate in the absence of the ionicliquid if the system goes through a (CO₂)⁻ intermediate. The reactioncoordinate indicates the fraction of the reaction that has beencompleted. A high potential for (CO₂)⁻ formation can create a highoverpotential for the reaction, which leads to enhanced hydrogenproduction.

FIG. 3 illustrates how the potential could change when a Helper Catalystis used. In this case the reaction could go through a CO₂ complex ratherthan a (CO₂)⁻ intermediate, substantially lowering the overpotential forthe reaction.

FIGS. 4 a, 4 b and 4 c illustrate some of the cations that can be usedto form a complex with (CO₂)⁻.

FIGS. 5 a and 5 b illustrate some of the anions that can help tostabilize the (CO₂)⁻ anion.

FIG. 6 illustrates some of the neutral molecules that can be used toform a complex with (CO₂)⁻.

FIG. 7 shows a schematic diagram of a cell used for the experiments intesting Catalytically Active Element, Helper Catalyst Mixtures, and inSpecific Examples 1 and 4 to 7.

FIG. 8 represents a comparison of the cyclic voltammetry for (i) a blankscan where the catalyst was synthesized as in the described testingprocedure for Catalytically Active Element, Helper Catalyst Mixtures,where the EMIM-BF4 was sparged with argon, and (ii) a scan where theEMIM-BF4 was sparged with CO₂. Notice the large negative peak associatedwith CO₂ complex formation.

FIG. 9 represents a series of Broad Band Sum Frequency Generation(BB-SFG) spectra taken sequentially as the potential in the cell wasscanned from +0.0 V to −1.2 V with respect to the standard hydrogenelectrode (SHE).

FIG. 10 shows a CO stripping experiment done by holding the potential at−0.6 V for 10 or 30 minutes and then measuring the size of the COstripping peak between 1.2 and 1.5 V with respect to the reversiblehydrogen electrode (RHE).

FIG. 11 Is a plot of the Faradaic efficiency of the process of formingthe desired CO and the undesired hydrogen, and the turnover rate as afunction of the applied cell potential for the cell in Specific Example3.

FIG. 12 shows a comparison of the cyclic voltammetry for (i) a blankscan where the catalyst was synthesized as in Specific Example 4 wherethe water-choline chloride mixture was sparged with argon and (ii) ascan where the water-choline chloride mixture was sparged with CO₂.

FIG. 13 represents a comparison of the cyclic voltammetry for (i) ablank scan where the catalyst was synthesized as in Example 5 where thewater-choline iodide mixture was sparged with argon and (ii) a scanwhere the water-choline iodide mixture was sparged with CO₂.

FIG. 14 shows a comparison of the cyclic voltammetry for (i) a blankscan where the catalyst was synthesized as in Example 6 where thewater-choline chloride mixture was sparged with argon and (ii) a scanwhere the water-choline chloride mixture was sparged with CO₂.

FIGS. 15 a and 15 b each show a plot of cyclic voltammetry of palladiumin the presence of different hydrogen suppressors. In each case thepotential is reported versus the measured value of RHE.

FIGS. 16 a and 16 b each show a plot of cyclic voltammetry of platinumin the presence of different hydrogen suppressors. In each case thepotential is reported versus the measured value of RHE.

FIGS. 17 a and 17 b each show a plot of cyclic voltammetry ofplatinum/ruthenium in the presence of different hydrogen suppressors. Ineach case the potential is reported versus the measured value of RHE.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

It is understood that the invention is not limited to the particularmethodology, protocols, and reagents, etc., described herein, as thesecan vary as the skilled artisan will recognize It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the invention. It also is to be noted that as used herein andin the appended claims, the singular forms “a”, “an”, and “the” includethe plural reference unless the context clearly dictates otherwise.Thus, for example, a reference to “a linker” is a reference to one ormore linkers and equivalents thereof known to those familiar with thetechnology involved here. Also, the term “and/or” is used to indicateone or both stated cases may occur, for example A and/or B includes (Aand B) and (A or B).

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which the invention pertains. The embodiments of thepresent invention and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments and/or illustrated in the accompanying drawings and detailedin the following description. It should be noted that the featuresillustrated in the drawings are not necessarily drawn to scale, andfeatures of one embodiment can be employed with other embodiments as theskilled artisan would recognize, even if not explicitly stated herein.

Any numerical value ranges recited herein include all values from thelower value to the upper value in increments of one unit provided thatthere is a separation of at least two units between a lower value and ahigher value. As an example, if it is stated that the concentration of acomponent or value of a process variable such as, for example, size,angle size, pressure, time and the like, is, for example, from 1 to 90,specifically from 20 to 80, more specifically from 30 to 70, it isintended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32etc., are expressly enumerated in this specification. For values whichare less than one, one unit is considered to be 0.0001, 0.001, 0.01 or0.1 as appropriate. These are only examples of what is specificallyintended and all possible combinations of numerical values between thelowest value and the highest value are to be treated in a similarmanner.

Moreover, provided immediately below is a “Definitions” section, wherecertain terms related to the present invention are defined specifically.Particular methods, devices, and materials are described, althoughmethods and materials similar or equivalent to those described hereincan be used in the practice or testing of the present invention. Allreferences referred to herein are incorporated by reference herein intheir entirety.

Definitions

The term “electrochemical conversion of CO₂” as used here refers to anelectrochemical process where carbon dioxide, carbonate, or bicarbonateis converted into another chemical substance in a step of the process.

The term “CV” as used here refers to a cyclic voltammogram or cyclicvoltammetry.

The term “Overpotential” as used here refers to the potential (voltage)difference between a reaction's thermodynamically determined reductionor oxidation potential and the potential at which the event isexperimentally observed.

The term “Cathode Overpotential” as used here refers to theoverpotential on the cathode of an electrochemical cell.

The term “Anode Overpotential” as used here refers to the overpotentialon the anode of an electrochemical cell.

The term “Electron Conversion Efficiency” refers to selectivity of anelectrochemical reaction. More precisely, it is defined as the fractionof the current that is supplied to the cell that goes to the productionof a desired product.

The term “Catalytically Active Element” as used here refers to achemical element that can serve as a catalyst for the electrochemicalconversion of CO₂ or another species of interest in a desired reaction.

The term “Helper Catalyst” refers to an organic molecule or mixture oforganic molecules that does at least one of the following: (a) speeds upa chemical reaction, or (b) lowers the overpotential of the reaction,without being substantially consumed in the process.

The term “Active Element, Helper Catalyst Mixture” refers to a mixturethat includes one or more Catalytically Active Element(s) and at leastone Helper Catalyst.

The term “Ionic Liquid” refers to salts or ionic compounds that formstable liquids at temperatures below 200 ° C.

The term “Deep Eutectic Solvent” refers to an ionic solvent thatincludes a mixture which forms a eutectic with a melting point lowerthan that of the individual components.

The term “Director Molecule” (or “Director Ion”) refers to a molecule orion that increases the selectivity of a reaction. If a director molecule(or ion) is added to a reaction mixture, the selectivity for a desiredreaction goes up. This effect may be the result of suppressing undesiredside reactions, even if the desired reaction is also slowed, as long asthe selectivity toward the desired reaction is increased.

The term “Hydrogen Suppressor” refers to a molecule that either: (a)decreases the rate of hydrogen formation, or (b) increases theoverpotential for hydrogen formation, when the molecule is added to areaction mixture.

The term “EMIM” refers to 1-ethyl-3-methylimidazolium.

The term “Carbon Dioxide Source” refers to a device or molecule that canprovide carbon dioxide to a system. The source may be in the form of abottle, packet, cartridge or other form. The Carbon Dioxide Source mayinclude gaseous, liquid, solid or supercritical carbon dioxide, andchemical compounds that can be easily converted to carbon dioxide suchas carbonates and bicarbonates.

The term “Pure Enough To Be Used In A Clinical Application” refers to agas mixture that a) includes carbon monoxide, b) has at least 10 timesas much carbon monoxide as hydrogen on a molar basis and c) has lessthan 1 ppm of any corrosive or toxic material other than carbonmonoxide.

Specific Description

The earlier related applications U.S. Ser. No. 12/830,338, U.S. Ser. No.13/174365, PCT/US11/42809, PCT/US11/30098 and provisional patentapplication U.S. 61/499,225 by Masel et al. described Active Element,Helper Catalyst Mixtures where the mixture does at least one of thefollowing: (1) speeds up a chemical reaction; or (2) lowers theoverpotential of the reaction, without being substantially consumed inthe process.

For example, such mixtures can lower the overpotential for CO₂conversion to a value less than the overpotential seen when the sameCatalytically Active Element is used without the Helper Catalyst.

In the course of exploring these Active Element, Helper CatalystMixtures, it was found that certain materials that were being tested asHelper Catalysts, such as salts of the choline cation(N,N,N-trimethylethanolammonium cation) and/or1-ethyl-3-methylimidazolium tetrafluoroborate could also raise theoverpotential for certain undesirable side reactions, including theevolution of hydrogen gas from electrolysis of water and the formationof side products such as acetic acid. As part of this effort, we foundthat it was possible to produce carbon monoxide electrochemically withpurity to meet the needs for a therapeutic carbon monoxide generatori.e. 20 times as much carbon monoxide as hydrogen, and less than 1 ppmof other byproducts. Further, one could precisely control the COdelivery rate by controlling the current or voltage applied to theelectrochemical cell.

Without wishing to be bound by theory, the present disclosure providesdata supporting the hypothesis that when a monolayer of an organiccompound is adsorbed on a metal surface, the presence of the organiccompound can change the binding energy of key intermediates of reactionsoccurring on (or near) the metal surface. This can lead to changes inreaction rates. For example, data herein suggests that the adsorption ofa cationic species such as a quaternary amine on an electrode (typicallythe negative electrode) of an electrochemical cell tends to stabilizeanionic intermediates and destabilize cationic intermediates inelectrochemical reactions. If the amine binds too strongly, it willsimply poison the surface, but if the binding strength is modest, rateenhancement is possible. Aliphatic quaternary amines would tend to bemerely electrostatically attracted to a metal electrode surface, sincethe positively charged nitrogen is sterically shielded by the aliphaticgroups and cannot interact directly with the metal surface. For the samereason, quaternary ammonium cations tend to be electrochemically stableacross a wide window of electrode potentials. Choline salts inparticular are commercially attractive quaternary amines, becausecholine chloride is a common food additive for livestock, and it is alsosold as a dietary supplement for humans. It is inexpensive, is readilyavailable, and presents minimal hazard. One could reasonably expect thatquaternary amine cations with structures similar to choline (forexample, structures in which one or more of the methyl groups on thenitrogen is replaced with other small aliphatic groups such as ethyl orpropyl groups) would behave in a fashion similar to the choline datadisclosed in the present application.

Ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate(EMIM-BF4) could also be used. Imidazoliums would tend to be merelyelectrostatically attracted to a metal electrode surface, since thepositively charged nitrogen is sterically shielded by the aliphaticgroups and cannot interact directly with the metal surface. They havevery low vapor pressures due to their ionic nature, so they could beused in systems for inhalation therapy.

According to the Hori review, Gattrell, et al. (Journal ofElectroanalytical Chemistry, 594, 1-19, 2006), DuBois (Encyclopedia ofElectrochemistry, 7a, 202-225, 2006) and references therein, catalystsincluding one or more of In, Sn, Cd, Zn, Au, Ag, Cu V, Cr, Mn, Fe, Co,Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au,Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd allshow activity for CO₂ conversion. Hori reports that only Au, Ag, Cu, Zn,Pd, In, Sn and Ga produce significant amounts of CO, but the datadisclosed in the specific examples in this patent shows that in thepresence of an appropriate helper catalyst, CO is produced on additionalmetals. Therefore, V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh,Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi,Sb, Te, U, Sm, Tb, La, Ce, and Nd are each examples of CatalyticallyActive Elements, but the present invention is not limited to this listof chemical elements.

FIGS. 2 and 3 illustrate one possible mechanism by which a HelperCatalyst can enhance the rate of CO₂ conversion to CO. According toChandrasekaran, et al. (Surface Science, 185, 495-514, 1987) the highoverpotentials for CO₂ conversion occur because the first step in theelectroreduction of CO₂ is the formation of a (CO₂)⁻ intermediate. Ittakes energy to form the intermediate as illustrated in FIG. 2. Thisresults in a high overpotential for the reaction.

FIG. 3 illustrates what might happen if a solution containing1-ethyl-3-methylimidazolium cations (EMIM⁺) is added to the mixture.EMIM⁺ might be able to form a complex with the (CO₂)⁻ intermediate. Inthat case, the reaction could proceed via the EMIM⁺-(CO₂)⁻ complexinstead of going through a bare (CO₂)⁻ intermediate as illustrated inFIG. 3. If the energy to form the EMIM⁺-(CO₂)⁻ complex is less than theenergy to form the (CO₂)⁻ intermediate, the overpotential for CO₂conversion could be substantially reduced. Therefore a substance thatincludes EMIM⁺ cations could act as a Helper Catalyst for CO₂conversion.

In most cases, solvents only have small effects on the progress ofcatalytic reactions. The interaction between a solvent and an adsorbateis usually much weaker than the interaction with a Catalytically ActiveElement, so the solvent only makes a small perturbation to the chemistryoccurring on metal surfaces. However, the diagram in FIG. 3 shows thatsuch an effect could be large.

Of course a Helper catalyst, alone, will be insufficient to convert CO₂to CO. Instead, one still needs a Catalytically Active Element that cancatalyze reactions of (CO₂)⁻ in order to get high rates of CO₂conversion. Catalysts including at least one of the followingCatalytically Active Elements have been previously reported to be activefor electrochemical conversion of CO₂: V, Cr, Mn, Fe, Co, Ni, Cu, Sn,Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si,In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd.

Many of these catalysts also show activity for a number of otherreactions. All of the above elements are specifically included asCatalytically Active Elements for the purposes of the present invention.This list of elements is meant for illustrative purposes only, and isnot meant to limit the scope of the present invention.

Further, those skilled in the technology involved here should realizethat the diagram in FIG. 3 could be drawn for any molecule that couldform a complex with (CO₂)⁻. Previous literature indicates that solutionsincluding one or more of: ionic liquids; deep eutectic solvents; andamines and phosphines, including specifically imidazoliums (also calledimidazoniums), pyridiniums, pyrrolidiniums, phosphoniums, ammoniums,prolinates, and methioninates, as well as sulfoniums, can form complexeswith CO₂. Consequently, they can serve as Helper Catalysts. Also DavisJr., et al. (in ACS Symposium Series 856: Ionic Liquids as GreenSolvents: Progress and Prospects, 100-107, 2003) list a number of othersalts that show ionic properties. Specific examples include compoundsincluding one or more of acetylcholines, alanines, aminoacetonitriles,methylammoniums, arginines, aspartic acids, threonines,chloroformamidiniums, thiouroniums, quinoliniums, pyrrolidinols,serinols, benzamidines, sulfamates, acetates, carbamates, triflates,alkali cations and cyanides. These salts can act as Helper Catalysts.These examples are meant for illustrative purposes only, and are notmeant to limit the scope of the present invention.

Of course, not every substance that forms a complex with (CO₂)⁻ will actas a Helper Catalyst. Masel (Chemical Kinetics and Catalysis, Wiley,pages 717-720, 2001,) notes that when an intermediate binds to acatalyst, the reactivity of the intermediate decreases. If theintermediate bonds too strongly to the catalyst, the intermediate willbecome unreactive, so the substance will not be effective. This providesa key limitation on substances that act as Helper Catalysts. The HelperCatalyst cannot form so strong a bond with the (CO₂)⁻ that the (CO₂)⁻ isunreactive toward the Catalytically Active Element or forms an undesiredstable reaction product with the material that was intended to be aHelper Catalyst.

More specifically, one wishes the substance to form a complex with the(CO₂)⁻ so that the complex is stable (that is, has a negative freeenergy of formation) at potentials less negative than −1 V with respectto the standard hydrogen electrode (SHE). However, the complex shouldnot be so stable that the free energy of the reaction between thecomplex and the Catalytically Active Element is more positive than about3 kcal/mol.

Those familiar with the technology involved here should realize that theability of the Helper Catalyst to stabilize the (CO₂)⁻ also varies withthe anion. For example Zhao, et al. (The Journal of SupercriticalFluids, 32, 287-291, 2004) examined CO₂ conversion in1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), but FIG. 3in Zhao, et al., shows that the BMIM-PF6 did NOT lower the overpotentialfor the reaction (that is, the BMIM-PF6 did not act as a HelperCatalyst). This may be because the BMIM-PF6 formed such a strong bond tothe (CO₂)⁻ that the CO₂ was unreactive with the copper. Similarly Yuan,et al., Electrochimica Acta 54, pages 2912-2915(2009), examined thereaction between methanol and CO₂ in 1-butyl-3-methylimidazolium bromide(BMIM-Br). The BMIM-Br did not act as a Helper Catalyst. This may bebecause the complex was too weak or that the bromine poisoned thereaction.

Solutions that include one or more of the cations in FIGS. 4 a, 4 b and4 c, the anions in FIGS. 5 a and 5 b, and/or the neutral species in FIG.6, where R₁, R₂ and R₃ (and R₄-R₁₇) include H, OH or a ligand containingat least one carbon atom, are believed to form complexes with CO₂ or(CO₂)⁻. Specific examples include: imidazoliums (also calledimidazoniums), pyridiniums, pyrrolidiniums, phosphoniums, ammoniums,sulfoniums, prolinates, and methioninates. All of these examples mightbe able to be used as Helper Catalysts for CO₂ conversion, and arespecifically included in the present invention. These examples are meantfor illustrative purposes only, and are not meant to limit the scope ofthe present invention.

In general one can determine whether a given substance S is a HelperCatalyst for a reaction R catalyzed by an active metal M as follows:

(a) Fill a standard 3-electrode electrochemical cell with theelectrolyte commonly used for reaction R. Common electrolytes such as0.1 M sulfuric acid or 0.1 M KOH in water can also be used.

(b) Mount the active metal into the 3 electrode electrochemical cell andprovide an appropriate counter electrode.

(c) Run several CV cycles to clean the active metal.

(d) Measure the reversible hydrogen electrode (RHE) potential in theelectrolyte.

(e) Load the reactants for the reaction R into the cell, and measure aCV of the reaction R, noting the potential of the peak associated withthe reaction R.

(f) Calculate V1=the difference between the onset potential of the peakassociated with reaction and RHE.

(g) Calculate V1A=the difference between the maximum potential of thepeak associated with reaction and RHE.

(h) Add 0.0001 to 99.9999% of the substance S to the electrolyte.

(i) Measure RHE in the reaction solution with Helper Catalyst.

(j) Measure the CV of reaction R again, noting the potential of the peakassociated with the reaction R.

(k) Calculate V2=the difference between the onset potential of the peakassociated with reaction and RHE.

(1) Calculate V2A=the difference between the maximum potential of thepeak associated with reaction and RHE.

If V2<V1 or V2A<V1A at any concentration of the substance S between0.0001 and 99.9999%, the substance S is a Helper Catalyst for thereaction.

Further, the Helper Catalyst could be in any one of the following forms:(i) a solvent for the reaction; (ii) an electrolyte; (iii) an additiveto a component of the system; or (iv) something that is bound to atleast one of the catalysts in a system. These examples are meant forillustrative purposes only, and are not meant to limit the scope of thepresent invention.

Those familiar with the technology involved here should recognize thatone might only need a tiny amount of the Helper Catalyst to have asignificant effect. Catalytic reactions often occur on distinct activesites. The active site concentration can be very low, so in principle asmall amount of Helper Catalyst can have a significant effect on therate. One can obtain an estimate of how little of the helper catalystwould be needed to change the reaction from the Pease, et al., JACS 47,1235 (1925) study of the effect of carbon monoxide (CO) on the rate ofethylene hydrogenation on copper. This paper is incorporated into thisdisclosure by reference. Pease, et al., found that 0.05 cc (62micrograms) of carbon monoxide (CO) was sufficient to almost completelypoison a 100 gram catalyst towards ethylene hydrogenation. Thiscorresponds to a poison concentration of 0.0000062% by weight of CO inthe catalyst. Those familiar with the technology involved here know thatif 0.0000062% by weight of the poison in a Catalytically ActiveElement-poison mixture could effectively suppress a reaction, then aslittle as 0.0000062% by weight of Helper Catalyst in an Active Element,Helper Catalyst Mixture could enhance a reaction. This provides anestimate of a lower limit to the Helper Catalyst concentration in anActive Element, Helper Catalyst Mixture.

The upper limit is illustrated in Example 1 below, where the ActiveElement, Helper Catalyst Mixture could have approximately 99.999% byweight of Helper Catalyst, and the Helper Catalyst could be at least anorder of magnitude more concentrated. Thus, the range of Helper Catalystconcentrations for the present invention can be 0.0000062% to 99.9999%by weight.

Further, the Helper Catalyst could enhance the rate of a reaction evenif it does not form a complex with a key intermediate. Examples ofpossible mechanisms of action include the Helper Catalyst (i) loweringthe energy to form a key intermediate by any means, (ii) donating oraccepting electrons or atoms or ligands, (iii) weakening bonds orotherwise making them easier to break, (iv) stabilizing excited states,(v) stabilizing transition states, (vi) holding the reactants in closeproximity or in the right configuration to react, or (vii) blocking sidereactions. Each of these mechanisms is described on pages 707-742 ofMasel, Chemical Kinetics and Catalysis, Wiley, NY (2001). All of thesemodes of action are within the scope of the present invention.

Also, the invention is not limited to just the catalyst. Instead itincludes a process or device that uses an Active Element, HelperCatalyst Mixture as a catalyst. Electrolytic cells and other devices toproduce CO that include Helper Catalysts or Hydrogen Suppressors arespecifically included in the present invention.

In particular it includes a device that includes an electrochemicaldevice for the production of CO that includes an Active Element andeither a Helper Catalyst and/or a Hydrogen Suppressor and a means todeliver the CO to a patient. The device may include a means to supplyCO₂ to the device. It may also include a CO sensor that allows the COconcentration to be accurately controlled.

A specific design is an inline cartridge that would be mounted betweenthe oxygen source and the patient. The cartridge would contain a sourceof CO₂ such as a carbonate or bicarbonate, an electrochemical cellincluding an Active Element and either a Helper Catalyst and/or aHydrogen Suppressor, and a CO sensor. It might include a battery andcontrol system.

Without further elaboration, it is believed that one skilled in the artusing the preceding description can utilize the present invention to thefullest extent. The following examples are illustrative only, and notlimiting of the disclosure in any way whatsoever. These are merelyillustrative and are not meant to be an exhaustive list of all possibleembodiments, applications or modifications of the present invention.

SPECIFIC EXAMPLE 1

The following section describes the testing procedure used for an ActiveElement, Helper Catalyst Mixture as previously disclosed in the relatedapplications cited above. These particular experiments measured theability of an Active Element, Helper Catalyst Mixture consisting ofplatinum and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) tolower the overpotential for electrochemical conversion of CO₂ to CO andraise the selectivity (current efficiency) of the reaction. Therefore,the test can determine whether EMIM-BF4 and the EMIM⁺ ion can serve asdirector molecules and director ions, respectively, for the desiredreaction. The desired reaction in this test will be the electrochemicalreduction of carbon dioxide (typically to primary products such as CO).

The experiments used the glass three electrode cell shown in FIG. 7. Thecell consisted of a three neck flask 101, to hold the anode 108, and thecathode 109. Seal 107 forms a seal around anode wire 108. Fitting 106compresses seal 107 around anode wire 108. Rotary seal 110 facilitatesrotation of shaft 111, which in turn causes gold plug 115 to spin. Seal119 closes the unused third neck of flask 101.

A silver/0.01 molar silver ion reference electrode 103 in acetonitrilewas connected to the cell through a Luggin Capillary 102, which includesa seal 117. The reference electrode 103 was fitted with a porous Vycorglass frit (available from Corning, Inc., Corning, N.Y., USA) to preventthe reference electrode solution from contaminating the ionic liquid inthe capillary. The reference electrode was calibrated against theferrocene Fc/Fc+ redox couple. A conversion factor of +535 was used toconvert our potential axis to reference the Standard Hydrogen Electrode(SHE). A 25×25 mm platinum gauze 113 (size 52) was connected to theanode while a 0.33 cm² polycrystalline gold plug 115 was connected tothe cathode.

Prior to the experiments all glass parts were put through a 1% Nochromixbath (2hrs) (available from Godax Laboratories, Inc., Cabin John, Md.,USA), followed by a 50/50 v/v nitric acid/water bath (12 hrs), followedby rinsing with Millipore filtered water (Millipore Corporation,Billerica, Mass., USA). In addition, the gold plug 115 and platinumgauze 113 were mechanically polished using procedures known to workerstrained in the technology involved here. The glass parts were thencleaned in a sulfuric acid bath for 12 hours.

During the experiment a catalyst ink comprising a Catalytically ActiveElement, platinum, was first prepared as follows: First 0.056 grams ofJohnson-Matthey Hispec 1000 platinum black purchased from Alfa-Aesar wasmixed with 1 gram of Millipore water and sonicated for 10 minutes toproduce a solution containing a 5.6 mg/ml suspension of platinum blackin Millipore water. A 25 μl drop of the ink was placed on the gold plug115 and allowed to dry under a heat lamp for 20 min, and subsequentlyallowed to dry in air for an additional hour. This yielded a catalystwith 0.00014 grams of Catalytically Active Element, platinum, on a goldplug. The gold plug was mounted into the three neck flask 101. Next aHelper Catalyst, EMIM-BF4 (EMD Chemicals, Inc., San Diego, Calif., USA)was heated to 120° C. under a −23 in. Hg vacuum for 12 hours to removeresidual water and oxygen. The concentration of water in the ionicliquid after this procedure was found to be approximately 90 mM byconducting a Karl-Fischer titration. (That is, the ionic liquidcontained 99.9999% of Helper Catalyst.) 13 grams of the EMIM-BF4 wasadded to the vessel, creating an Active Element, Helper Catalyst Mixturethat contained about 99.999% of the Helper Catalyst. The geometry wassuch that the gold plug formed a meniscus with the EMIM-BF4. Next,ultra-high-purity (UHP) argon was fed through the sparging tube 104 andglass frit 112 for 2 hours at 200 sccm to further remove any moisturepicked up by contact with the air. Connector 105 was used to attach thecell to a tube leading to the gas source.

Next, the cathode was connected to the working electrode connection inan SI 1287 Solartron electrical interface (Solartron Analytical,Schaumburg, Ill., USA), the anode was connected to the counter electrodeconnection and the reference electrode was connected to the referenceelectrode connection on the Solartron. Then the potential on the cathodewas swept from −1.5 V versus a standard hydrogen electrode (SHE) to 1 Vvs. SHE, and then back to −1.5 volts versus SHE thirty times at a scanrate of 50 mV/s. The current produced during the last scan is labeled asthe “argon” scan in FIG. 8.

Next carbon dioxide was bubbled through the sparging tube at 200 sccmfor 30 minutes, and the same scanning technique was used. That producedthe CO₂ scan in FIG. 8. Notice the peak starting at −0.2 volts withrespect to SHE, and reaching a maximum at −0.4 V with respect to SHE.That peak is associated with CO₂ conversion.

The applicants have also used broad-band sum frequency generation(BB-SFG) spectroscopy to look for products of the reaction, as shown inFIG. 9. Only the desired product carbon monoxide was detected in thevoltage range shown (namely, the selectivity is about 100%). Oxalic acidwas detected at higher potentials.

Table 1 compares these results to results from the previous literature.The table shows the actual cathode potential. More negative cathodepotentials correspond to higher overpotentials. More precisely, theoverpotential is the difference between the thermodynamic potential forthe reaction (about −0.2 V with respect to SHE) and the actual cathodepotential. The values of the cathode overpotential are also given in thetable. Notice that the addition of the Helper Catalyst has reduced thecathode overpotential (namely, lost work) on platinum by a factor of 4.5and improved the selectivity from near zero to nearly 100%.

TABLE 1 (Comparison of data in this test to results reported in previousliterature) Cathode Selectivity to Catalytically potential CathodeCarbon Reference Active Element versus SHE overpotential Monoxide Datafrom Platinum  −0.4 V  0.2 V ~100% this test (+EMIM-BF₄) Hori reviewPlatinum −1.07 V 0.87 V   0.1% Table 3 (+water)

TABLE 2 (Cathode potentials where CO₂ conversion starts on a number ofCatalytically Active Elements as reported in the Hori review). CathodeCathode Cathode potential potential potential Metal (SHE) Metal (SHE)Metal (SHE) Pb −1.63 Hg −1.51 Tl −1.60 In −1.55 Sn −1.48 Cd −1.63 Bi−1.56 Au −1.14 Ag −1.37 Zn −1.54 Pd −1.20 Ga −1.24 Cu −1.44 Ni −1.48 Fe−0.91 Pt −1.07 Ti −1.60

Table 2 indicates the cathode potential needed to convert CO₂. Noticethat all of the values are more negative than −0.9 V. By comparison,FIG. 8 shows that CO₂ conversion starts at −0.2 V with respect to thereversible hydrogen electrode (RHE), when the Active Element, HelperCatalyst Mixture is used as a catalyst. More negative cathode potentialscorrespond to higher overpotentials. This is further confirmation thatActive Element, Helper Catalyst Mixtures are advantageous for CO₂conversion.

FIG. 9 shows a series of broad band sum-frequency generation (BB-SFG)spectra taken during the reaction. Notice the peak at 2350 cm⁻¹. Thispeak corresponded to the formation of a stable complex between theHelper Catalyst and (CO₂)⁻. It is significant that the peak starts at−0.1 V with respect to SHE. According to the Hori review, (CO₂)⁻ isthermodynamically unstable unless the potential is more negative than−1.2 V with respect to SHE on platinum. Yet FIG. 9 shows that thecomplex between EMIM-BF4 and (CO₂)⁻ is stable at −0.1 V with respect toSHE.

Those familiar with the technology involved here should recognize thatthis result is very significant. According to the Hori review, theDubois review and references therein, the formation of (CO₂)⁻ is therate determining step in CO₂ conversion to products on V, Cr, Mn, Fe,Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt,Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd.The (CO₂)⁻ is thermodynamically unstable at low potentials, which leadsto a high overpotential for the reaction as indicated in FIG. 2. Thedata in FIG. 9 shows that one can form the EMIM-BF4-(CO₂)⁻ complex atlow potentials. Thus, the reaction can follow a low energy pathway forCO₂ conversion to CO as indicated in FIG. 3.

The Effect of Dilution on the Electrochemical Conversion of CO₂

This experiment shows that water additions speed the formation of CO inthe previous reaction. The experiment used the cell and proceduresdescribed above, with the following exception: a solution containing98.55% EMIM-BF4 and 0.45% water was substituted for the 99.9999%EMIM-BF4 used in the experiment above, the potential was held for 10 or30 minutes at −0.6 V with respect to RHE, and then the potential wasramped positively at 50 mV/sec. FIG. 10 shows the result. Notice thepeak between 1.2 and 1.5 V. This is the peak associated with COformation and is much larger than in the first experiment above. Thusthe addition of water has accelerated the formation of CO. Notice alsothat there is no hydrogen peak in the spectrum. This result shows thatEMIM-BF4 can be used as a Hydrogen Suppressor.

SPECIFIC EXAMPLE 2 Steady State Production of Carbon Monoxide

This experiment used the flow cell described in Devin T. Whipple, E. C.Finke, and P. J. A. Kenis, Electrochem. & Solid-State Lett., 2010, 13(9), B109-B111 (“the Whipple paper”). First, catalyst inks were preparedas follows:

For the cathode: 10 mg of silver nanoparticles (Sigma Aldrich) wassonicated into a solution containing 100 μL of water, 100 μL ofisopropyl alcohol and 5.6 μL of 5% perfluorosulfonic acid solution(available under the trade designation Nafion, from Ion Power, Inc., NewCastle, Del., USA). The resultant catalyst ink was painted on a 1×1.5 cmsection of a 2×3 cm piece of carbon paper (Ion Power, Inc.) and driedwith a heat lamp.

The preparation was identical for anode except 4 mg of HiSpec 1000platinum black (Sigma Adrich) was substituted for the silver.

Both catalysts were mounted in the flow cell described in the WhipplePaper. Five sccm of CO₂ was fed to the anode, and a solution containing18 mole percent of EMIM-BF4 in water was fed into the gap between theanode and the cathode. At any one time the cell contained approximately10 mg of silver nanoparticles and approximately 40 mg of EMIM-BF4 HelperCatalyst. A potential was applied to the cell, and the data in Table 3were measured with a gas chromatograph. Notice that at higher potentialsone is able to produce about 0.5 mg/min of CO, without significanthydrogen or other by products. Further, notice that one can preciselycontrol the CO production rate by carefully adjusting the voltage (orapplied current). This has the key advantage.

These results demonstrate that steady state production of usefulproducts can be obtained with Catalytically Active Element-HelperCatalyst Mixtures. It is believed that choline salts or other HelperCatalysts that suppress hydrogen evolution could be readily substitutedfor the Helper Catalyst EMIM-BF4.

TABLE 3 (Products produced at various conditions) Hydrogen Carbonmonoxide Cathode potential production rate, production rate, Volts vs.RHE μg/min μg/min CO/H₂ ratio −0.358 0 0 −0.862 1.1 2.6 2.4 −1.098 1.450 35 −1.434 1.1 250 230 −1.788 0 560 >1000

SPECIFIC EXAMPLE 3 High Quality Carbon Monoxide Production Over a WideRange of Rates

Example 2 showed that CO could be produced at high rates andselectivities, but when the voltage was decreased, so the ratedecreased, the CO₂ to hydrogen ratio was less than 20. This could createa problem in clinical systems where there is a need to produce carbonmonoxide over a wide range of rates. This example describes a modifieddesign that allows one to produce pure carbon monoxide over a widerrange of conditions.

The apparatus and procedures were the same as in Specific Example 2,except that a Nafion 117 membrane (available from Ion Power, Inc.) wasinserted between the cathode and the anode to create separate anode andcathode compartments. The anode compartment contained 100 mM aqueoussulfuric acid flowing at 0.5 ml/min. The cathode compartment contained18 mol % EMIM-BF₄ in water at 0.5 ml/min. A potential was applied to thecell, and the data in FIG. 11 were measured with a gas chromatograph.Experimentally, only hydrogen, CO and CO₂ were detected at the cathodeand only O₂ was detected at the anode. In all cases there was more than20 times as much CO as H₂ and no other reaction products were detectedwith the gas chromatograph. This result shows that it is possible tocreate carbon monoxide electrochemically with enough purity to be usedin clinical applications.

SPECIFIC EXAMPLE 4 Use of an Active Element, Helper Catalyst MixtureThat Includes Nickel and Choline Chloride to Lower the Overpotential forElectrochemical Conversion of CO₂ to CO and Suppress Hydrogen Formation

This example is to demonstrate that the present invention can bepracticed using a second metal, namely, nickel and a second helpercatalyst, choline chloride.

The experiment used the cell and procedures described in SpecificExample 1 above, with the following exceptions: i) a 10.3% by weight ofa Helper Catalyst, choline iodide, in water solution was substituted forthe 1-ethyl-3-methylimidazolium tetrafluoroborate and ii) a 0.25 cm² Nifoil purchased from Alfa Aesar of Ward Hill, Mass., USA, was substitutedfor the gold plug and platinum black on the cathode, and a silver/silverchloride reference was used.

The cell contained 52 mg of nickel and 103 mg of helper catalyst, so theoverall catalyst mixture contained 66% of helper catalyst.

FIG. 12 shows a comparison of the cyclic voltammetry for i) a blank scanwhere the water-choline chloride mixture was sparged with argon and ii)a scan where the water-choline chloride mixture was sparged with CO₂.Notice the negative going peaks starting at about −0.6. This shows thatCO₂ is being reduced at −0.6 V. By comparison, the data in Table 2indicates that a voltage more negative than −1.48 V is needed to convertCO₂ on nickel in the absence of the Helper Catalyst. Thus, the HelperCatalyst has lowered the overpotential for CO₂ conversion.

Another important point is that there is no strong peak for hydrogenformation. A bare nickel catalyst would produce a large hydrogen peak atabout −-0.4 V at a pH of 7, while the hydrogen peak moves to −1.2 V inthe presence of the Helper Catalyst. The Hori review reports that nickelis not an effective catalyst for CO₂ reduction because the side reactionproducing hydrogen is too large. The data in FIG. 12 show that theHelper Catalysts are effective in suppressing hydrogen formation.

Also the Helper Catalyst is very effective in improving the selectivityof the reaction. The Hori review reports that hydrogen is the majorproduct during carbon dioxide reduction on nickel in aqueous solutions.The reported hydrolysis data shows 1.4% selectivity to formic acid, andno selectivity to carbon monoxide. By comparison, analysis of thereaction products in this example by CV indicated that carbon monoxidewas the major product during CO₂ conversion on nickel in the presence ofthe Helper Catalyst. There may have been some formate formation.However, no hydrogen was detected. This example shows that the HelperCatalyst had tremendously enhanced the selectivity of the reactiontoward CO.

This example also demonstrates that the present invention can bepracticed with a second metal, nickel, and a second helper catalyst,choline chloride. Further, those familiar with the technology involvedhere will note that there is nothing special about the Active Element,Helper Catalyst pair of nickel and choline chloride.

Those familiar with the technology involved here should realize thatsince choline chloride and choline iodide (in Specific Example 5 below)are active, other choline salts such as choline bromide, cholinefluoride and choline acetate should be active as well.

PREDICTIVE EXAMPLES OF DIRECTOR MOLECULES AND DIRECTOR IONS

The applicants believe that to serve as a director molecule (or ion) forpurposes such as suppressing hydrogen evolution in an electrochemicalcell, the chemical species should have at least one positively chargedgroup and at least one group for surface attachment (for example, forattachment to the negative electrode). In other words, what is needed isa positively charged species with something to hold the positive chargenear the surface, but not to bind so strongly that the surface ispoisoned. A number of alcohols, aldehydes, ketones, and carboxylic acidsshould work, although some carboxylic acids might bind too tightly tothe electrode surface, and may thus poison the desired reaction.Similarly, other polar groups in addition to —OR, —COR, and —COOR, suchas —NR₂, —PR₂, —SR and halides, where the R groups can independently behydrogen or ligands containing carbon, (with the possible exception ofcarboxylic acid groups and their salts,) could serve as satisfactorysurface attachment groups. For the positively charged group, a varietyof amines and phosphoniums should be satisfactory. The key is to add anattached group to bind them to the surface, and the positive group(s)should not be so large as to be hydrophobic. Methyl, ethyl and propylquaternary amines should perform well. Imidazoliums (sometimes alsocalled imidazoniums) should also be satisfactory, provided they containan attachment group. Potassium and cesium cations could also work, sincepotassium and cesium can attach to the surface under certain conditions.A significant aspect of the present invention is the identification ofmolecules or ions that can serve as both Helper Catalysts (acceleratingor lowering the overpotential for desired reactions) and directormolecules (increasing the selectivity toward the desired reaction, forexample, by poisoning undesired reactions more than the desiredreaction).

COMPARATIVE EXAMPLE 1 Use of an Active Element, Helper Catalyst MixtureIncluding Palladium and Choline Iodide to Lower the Overpotential forElectrochemical Conversion of CO₂ in Water and Suppress HydrogenFormation

This example is to demonstrate that hydrogen can be suppressed usingpalladium as an active element and choline iodide as a Helper Catalyst,but formic acid formation occurs.

The experiment used the cell and procedures described in SpecificExample 1, with the following exceptions: i) a 10.3% by weight of aHelper Catalyst, choline iodide, in water solution was substituted forthe 1-ethyl-3-methylimidazolium tetrafluoroborate and ii) a 0.25 cm² Pdfoil purchased from Alfa Aesar of Ward Hill, Mass., USA, was substitutedfor the gold plug and platinum black on the cathode, and a silver/silverchloride reference was used.

The cell contained 52 mg of palladium and 103 mg of helper catalyst, sothe overall catalyst mixture contained 66% of helper catalyst.

FIG. 13 shows a CV taken under these conditions. There is a largenegative peak near zero volts with respect to SHE associated with iodinetransformations and a negative going peak at about −0.8 V associatedwith conversion of CO₂. By comparison the data in Table 2 indicates thatone needs to use a voltage more negative than −1.2 V to convert CO₂ onpalladium in the absence of the Helper Catalyst. Thus, the HelperCatalyst has lowered the overpotential for CO₂ formation by about 0.5 V.

Unfortunately, analysis of the products of the reaction showed that asignificant amount of formic acid was formed. Therefore, this catalystsystem would not be preferred for generation of carbon monoxide.

COMPARATIVE EXAMPLE 2 Use of an Active Element, Helper Catalyst MixtureThat Includes Palladium and Choline Chloride to Suppress HydrogenFormation

This example is to demonstrate that hydrogen can be suppressed usingpalladium as an active element and choline chloride as a HelperCatalyst, but formic acid formation occurs.

The experiment used the cell and procedures in Counter Example 1, withthe following exception: a 6.5% by weight choline chloride in watersolution was substituted for the choline iodide solution.

The cell contained 52 mg of palladium and 65 mg of Helper Catalyst, sothe overall catalyst mixture contained 56% of Helper Catalyst. FIG. 14shows a comparison of the cyclic voltammetry for (i) a blank scan wherethe water-choline chloride mixture was sparged with argon and (ii) ascan where the water-choline chloride mixture was sparged with CO₂.Notice the negative going peaks starting at about -0.6. This shows thatCO₂ is being reduced at −0.6 V. By comparison the data in Table 2indicates that a voltage more negative than −1.2 V is needed to convertCO₂ on palladium in the absence of the Helper Catalyst. Thus, theoverpotential for CO₂ conversion has been lowered by 0.6 V by the HelperCatalyst.

Another important point is that there is no strong peak for hydrogenformation. A bare palladium catalyst would produce a large hydrogen peakat about −0.4 V at a pH of 7, while the hydrogen peak moves to −1.2 V inthe presence of the Helper Catalyst. The Hori review reports thatpalladium is not an effective catalyst for CO₂ reduction because theside reaction producing hydrogen is too large. The data in FIG. 12 showthat the Helper Catalysts are effective in suppressing hydrogenformation. The same effect can be observed in FIG. 13 for the cholineiodide solution on palladium in Comparative Example 1

Cyclic voltammetry was also used to analyze the reaction products.Formic acid was the only product detected. By comparison, the Horireview reports that the reaction is only 2.8% selective to formic acidin water. Thus the Helper Catalyst has substantially improved theselectivity of the reaction to formic acid. Unfortunately, formic acidis not preferred for therapeutic applications.

SPECIFIC EXAMPLE 5 (Demonstration of Hydrogen Suppression With OtherCholine Derivatives)

The experiments were the same as in Specific Example 4, except that oneof (a) choline acetate, (b) choline BF4, (c)(3-chloro-2-hydroxypropyl)trimethyl ammonium chloride, (d)butyrylcholine chloride, and (e) (2-chloroethyl)trimethylammoniumchloride were used instead of choline chloride (which is also shown herefor comparison.) FIGS. 15 a, 15 b, 16 a, 16 b, 17 a and 17 b show CVstaken as described in Specific Example 1 on platinum, palladium andplatinum/ruthenium catalysts. Note that these CVs are plotted vs. RHE,rather than vs. SHE as in FIGS. 8, 10, and 12-14. In all cases hydrogenevolution is expected at 0V with respect to RHE, but negligiblehydrogens observed. This result shows that (a) choline acetate, (b)choline BF4, (c) (3-chloro-2-hydroxypropyl)trimethyl ammonium chloride,(d) butyrylcholine chloride, and (e) (2-chloroethyl)trimethylammoniumchloride are all hydrogen suppressors.

The examples given above are merely illustrative and are not meant to bean exhaustive list of all possible embodiments, applications ormodifications of the invention. Thus, various modifications andvariations of the described methods and systems of the invention will beapparent to those skilled in the art without departing from the scopeand spirit of the invention. Although the invention has been describedin connection with specific embodiments, it should be understood thatthe invention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled in thechemical arts or in the relevant fields are intended to be within thescope of the appended claims.

The disclosures of all references and publications cited above areexpressly incorporated by reference in their entireties to the sameextent as if each were incorporated by reference individually.

While particular elements, embodiments and applications of the presentinvention have been shown and described, it will be understood that theinvention is not limited thereto, since modifications can be made bythose skilled in the art without departing from the scope of the presentdisclosure, particularly in light of the foregoing teachings.

What is claimed is:
 1. An carbon monoxide generator for chemicallaboratory or therapeutic uses, comprising a. A Carbon Dioxide Source,and b. A means to convert carbon dioxide to carbon monoxide, wherein theoutput of the carbon monoxide generator contains at least 20 times asmuch CO as H₂ on a molar basis.
 2. The carbon monoxide generator inclaim 1 with a Carbon Dioxide Source comprising at least one of solidCO₂, liquid CO₂, gaseous CO₂, a carbonate or a bicarbonate.
 3. Thecarbon monoxide generator in claim 1 comprising an electrochemical cell4. The carbon monoxide generator in any of the preceding claims,comprising at least one of a) a Helper Catalyst b) A Directing Moleculeor c) a Hydrogen Suppressor.
 5. The Carbon Dioxide Source in claim 1comprising at least one of a) a Helper Catalyst b) A Directing Moleculeor c) a Hydrogen Suppressor.
 6. The device in claim 4 or 5, with atleast one of a) the Helper Catalyst, b) The Directing Molecule or c) theHydrogen Supressor comprising at least one cation and/or at least oneanion.
 7. The device in any of claim 4, 5, or 6 wherein at least one ofa) the Helper Catalyst, b) The Directing Molecule or c) the HydrogenSupressor has a concentration of between about 0.000006 2% and 99.999%by weight.
 8. The device of any of claims 4-7, wherein at least one ofa) the Helper Catalyst, b) The Directing Molecule or c) the HydrogenSupressor comprises at least one of the following: phosphines,imidazoliums, pyridiniums, pyrrolidiniums, phosphoniums, sulfoniums,prolinates, methioninates, or alkali ions.
 9. The device of any ofclaims 4-8, wherein at least one of a) the Helper Catalyst, b) TheDirecting Molecule or c) the Hydrogen Supressor comprises cholines or acholine salt.
 10. The device of any one of claims 4 through 9 wherein atleast one of a) the Helper Catalyst, b) The Directing Molecule or c) theHydrogen Supressor comprises 1-ethyl-3-methylimidazolium cations. 11.The device of any of claims 4 through 10 wherein at least one of a) theHelper Catalyst, b) The Directing Molecule or c) the Hydrogen Supressorcomprises tetrafluoroborate anions.
 12. The device of any of claims 4through 11, wherein at least one of a) the Helper Catalyst, b) TheDirecting Molecule or c) the Hydrogen Supressor comprises potassium orcesium cations.
 13. The device of any of claims 4 through 12, wherein atleast one of a) the Helper Catalyst, b) The Directing Molecule or c) theHydrogen Supressor comprises tetrafluoroborate anions, and is a solvent,electrolyte or additive.
 14. The device of any of claims 4 through 13above, wherein the Director Molecule comprises:a positively chargesspecies further comprising at least one polar group selected from —OR,—COR, —COOR, —NR₂, —PR₂, —SR, or halides, where the R groups canindependently be hydrogen or ligands containing carbon.
 15. The deviceof any of claims 4 through 14 above, wherein the Hydrogen Suppressorcomprises: a choline derivative of the form R₁R₂R₃N⁺ (CH₂)_(n)OH orR₁R₂R₃N⁺ (CH₂)_(n)Cl, wherein n=1-4, and R₁, R₂, and R₃ areindependently selected from the group consisting of aliphatic C₁-C₄groups, —CH₂OH, —CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH,—CH₂CH₂COH, and —CH₂COCH₃ and molecules where one or more chlorine orfluorine is substituted for hydrogen in aliphatic C₁-C₄ groups, —CH₂OH,—CH₂CH₂OH, —CH₂CH₂CH₂OH, —CH₂CHOHCH₃, —CH₂COH, —CH₂CH₂COH, or —CH₂COCH₃.16 A portable carbon monoxide generator for chemical laboratory ortherapeutic use, comprising the device of any of the above claims. 16.The device of any of claims 2 through 14 above wherein the devicecomprises a cartridge that fits in the line between an oxygen source anda patient.
 17. A method of producing carbon monoxide for chemicallaboratory or therapeutic uses, comprising the steps of: providing thedevice of any of the above claims; providing carbon dioxide, acarbonate, or a bicarbonate from the Carbon Dioxide Source to thedevice; providing any additional water, solvent, or electrolyte as maybe needed; applying a source of energy, such as an electric current, tothe device; and directing the carbon monoxide thus produced to theintended point of use.